DARLING RIVERINE PLAINS BIOREGION Background Report

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16/08/02 Darling Riverine Plains Bioregion Background Report Variation in temperature and rainfall across the bioregion has also been modelled from the digital elevation model. The mapping shows that the variation in climatic variables is not affected by variation in local relief. 2.2.1 Rainfall: temporal and spatial variation Most of the bioregion occurs within the summer rainfall region of New South Wales, with higher and more reliable rainfalls occurring in the east. The mean monthly rainfall ranges from about 60 mm in the east of the bioregion to 15 mm in the west and along most of the Darling River (Map 14). At the six meteorological stations, mean annual rainfall ranges from 578.6 mm at Moree to 508.3 mm at Mungindi, 504.8 mm at Trangie, 477.8 mm at Walgett, 355.1 mm at Bourke and 243.7 mm at Menindee (Bureau of Meteorology 2001). These mean values, however, mask the fact that the rainfall in the bioregion is highly variable in frequency and intensity and is generally unreliable. There are occasional periods of intense rainfall, which are often the products of deep extra-tropical depressions. Large portions of the bioregion also experience prolonged periods of no rainfall. The annual rainfall recorded at Bourke from 1871, graphed on Figure 2.1, illustrates this variability, with annual total rainfall ranging from about 80mm to 850mm. This variability is also demonstrated by the mean and first and ninth deciles calculated for the Bourke’s monthly rainfall averages (Figure 2.2). The first decile is the rainfall amount not exceeded by the lowest 10% of rainfall events. The ninth decile is the rainfall amount exceeded by the highest 10% of rainfall events. The first and ninth decile are measured to give the ‘normal’ rainfall range (that which 80% of all rainfall events falls within). The rainfall at Mungindi in the north east of the bioregion has a more definite summer pattern with January and February being the wettest months. The range between the first and ninth deciles is also greatest for those months (Figure 2.3). This contrasts with Menindee in the southwest (Figure 2.4) and Trangie in the southeast (Figure 2.5) where there is no evidence of summer dominance in the rainfall although the range between the first and ninth deciles is greatest in December and January. Monthly means and ranges, which illustrate the degree of rainfall variability, have also been calculated for Walgett in the centre of the bioregion (Figure 2.6). The distribution and intensity of rainfall is also illustrated by median monthly rainfall (Figure 2.7) and mean monthly rain days (Figure 2.8) (Bureau of Meteorology 2001). Mean monthly rainfall and mean monthly rainfall graphs for each of these weather stations across the DRP are shown in Appendix A. 30
ainfall (mm) 900 800 700 600 500 400 300 200 100 16/08/02 Darling Riverine Plains Bioregion Background Report 0 1871 1877 mm 120 100 80 60 40 20 0 1883 1889 1895 1901 1907 Bourke mean annual rainfall 1913 1919 1925 1931 Figure 2.1 Annual rainfall records for Bourke 1871-1999 Bourke mean monthly rainfall Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec month Figure 2.2 Bourke mean monthly rainfall and range between first and ninth decile (Bureau of Meteorology 2001) 1937 year 1943 1949 1955 1961 1967 1973 1979 1985 1991 31
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Initial Phase Assessment Phase 16/0
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Appendix A: Mean Monthly Rainfall a
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Major Rangetype Rangetype Physiogra
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Appendix C : Native Flora Other Tha
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Family Scientific Name Common Name
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Family Scientific Name cretica Comm
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APPENDIX E: Fauna Other than Those
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Common Name Scientific Name No Reco
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Common 1983 1984 1985 1986 1987 198
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Taxa No Records Dataset Class Arach
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Taxa No Records Dataset Tabanidae s
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Taxa No Records Dataset Berosus sp
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DARLING RIVERINE PLAINS BIOREGION Background Report

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